Auditory efferents shape afferent auditory processing. The normative features of the medial olivocochlear (MOC) efferent effects and their functional significance in children are not known. Although the MOC reflex is mature around full-term birth, evidence suggests that its strength can be altered through short-term training and experiences. The overall goal of the proposed work is to characterize features of the MOC reflex and investigate its functional significance in auditory perception in typically developing, normal-hearing children. The central hypothesis is that the MOC strength is important for listening in noise during development and that auditory attention plays a prominent role in modulating MOC activity. A combination of perceptual and physiologic (otoacoustic emissions) tests will be used in this project. In Specific Aim 1, the distribution or continuum of the MOC reflex strength, measured via innovative and refined click evoked OAE methods, will be characterized in children. It is predicted that robust measurements of the MOC reflex can be obtained that will allow for observing subtle changes in the MOC reflex due to experimental manipulation. The MOC reflex is expected to show a normal variation in strength from weak to strong across normal hearing children. Further controlling auditory attention is expected to alter the size of th MOC reflex and may reduce the variability among children. Data from adults will be obtained for comparison. In Specific Aim 2, the relationship between the MOC reflex and auditory perception in noise will be investigated in children and adults. Specifically, performance in frequency discrimination in noise will be correlated with the magnitude of the MOC reflex measured in no-task and auditory task conditions. A significant correlation is expected between the strength of the MOC reflex (measured in the auditory task condition) and auditory perception in both children and adults. The long-term goal of the proposed research is to understand the role of efferent mechanisms in auditory perceptual development. The MOC tests developed in this work should be useful both clinically and scientifically in the diagnosis and monitoring of auditor disorders (specifically listening-in-noise deficits), may guide habilitative (training) efforts, an should demonstrate the role of MOC feedback during development.